1. Field of the Invention
The present invention relates to a yarn delivery method, and more particularly to a uniform yarn delivery method and apparatus for a circular knitting machine.
2. Description of Related Art
Fabric consists of many loops (i.e., warp and weft). A uniform loop is key to a high quality fabric. Further, the uniform loop is determined by a good knitting process. As such, a stable and uniform yarn delivery is an object to be achieved by fabric manufacturers.
Conventionally, yarn supply device is for providing a stable and uniform yarn delivery. In comparing a simple yarn supply drum with a storing drum, the latter has a better yarn delivery capability. However, the storing drum may suffer at least one of the problems such as yarn winded on drum not uniformly delivered toward the lower position, loops entangled, and dislocation of loops. Further, the yarn tension detection arm of the storing drum presses on yarn by its weight only. The yarn tension detection arm is stopped immediately after yarn tension disappears. However, this technique is outdated because 1) it cannot accommodate high speed knitting requirements today, and 2) the yarn tension detection arm is not sufficiently sensitive. As such, fabric knitted by a knitting machine equipped with such a storing drum is poor in quality. Thus it is not acceptable by the fabric manufacturing art.
In a typical yarn delivery technique, tension of yarn is related to cam position of the knitting machine. Conventionally, yarn is made as taut as possible before entering the knitting machine so as to enhance yarn tension, thereby obtaining loops with uniform tension and identical size. However, it is impossible to visually determine the uniformity of yarn tension because, as stated above, the yarn tension detection arm is activated by its weight (i.e., non-adjustable) and yarn is too taut. In fact, the cam position usually is adjusted by an experienced operator. The operator often adjusts the yarn tension to its maximum. As a result, fabric quality is poor as manufactured by high speed knitting machines. Further, a variety of disadvantages such as short pitch, small loop, breakage, dislocation, rough, poor quality, low elasticity, and high contraction are experienced.